1. Field of the Invention
The present invention relates to an apparatus for detecting and measuring various biological information generated by the body of a subject, and particularly it relates to a biomagnetic field-measuring apparatus for measuring at a high precision the strength of weak magnetic fields generated by organs such as the brain, arms, eyeballs and heart.
2. Description of the Related Art
The human body generates a variety of biological information in response to changes in the external environment, and as used herein, the term "biological information" refers not only to physiological quantities generated by the body, but also includes the absorption of X-rays and magnetism.
An X-ray tomographic apparatus, known as an X-ray CT scanner, provides two-dimensional cross-sectional images from the X-ray absorption-.of sections of the body, and the images enable the diagnosis of diseases of the head and abdomen.
A magnetic resonance computed tomography apparatus, known as an MRI apparatus, provides information on the resonance absorption of hydrogen or carbon atoms, which reflects their electronic state, particularly enabling the diagnosis of oncocytes.
Biomagnetic field-measuring apparatuses, also known as MEG apparatuses, detect extremely weak biomagnetism of 10.sup.-12 T or less from human organs, and they are useful for preparing magnetoencephalograms and magnetoencephalograms and may thus be used for the diagnosis of epilepsy, encephalopathy, etc. These measuring apparatuses are all weighty, especially biomagnetic field-measuring apparatuses which have a total of weight of about 200 kgf.
In general, supporting means suspends biomagnetic field-measuring means from the ceiling, which is more subject vibration than the floor, and whose vibration is difficult to prevent.
Another typical prior technique employs a construction in which magnetic field-measuring means is mounted on an rocking arm anchored to the wall, etc. of a magnetically shielded room. With this technique, it is difficult to support the magnetic field-measuring means so that it does not vibrate.
Also, in an embodiment disclosed in Japanese Unexamined Patent Publication (KOKAI) JP-A 2-116767 (1990), the foundation of the magnetically shielded room is enlarged, and a supporting pillar is provided to directly connect the foundation of the magnetically shielded room with the supporting means. This construction is a very effective means of preventing vibration, but there is no mechanical connection between the magnetically shielded room and the supporting means, and thus the rigidity and mass of the magnetically shielded room are not efficiently utilized. Furthermore, a large hole must be made in the magnetically shielded room, and this result in lower shielding performance.
Since only a portion of the magnetic fields has conventionally been sampled when measuring biomagnetic fields, a requisite has been an increase in the degree of freedom of the supporting means which supports the biomagnetic field-measuring means which detects the magnetic field, and consequently it has been difficult to increase the frequency of vibration of the normal mode of the supporting means.
With this type of biomagnetic field-measuring apparatus, when detecting the strength of magnetic fields generated from the body using a fluxmeter which employs a superconducting quantum interference device (SQUID), when the fluxmeter vibrates undesirably it moves across the surrounding magnetic field, thus generating noise. Therefore, controlling the amplitude of the fluxmeter so that it does not vibrate results in controlling the noise. The vibration energy is proportional to the square of the amplitude and the square of the frequency. By raising the frequency (natural) to greatly reduce the amplitude, it is possible to lower the level of noise.